DE69828812T2 - METHOD FOR THE PRODUCTION OF CALENDERED PAPER - Google Patents

Abstract

A method and apparatus for producing calendered paper by an on-line manufacturing system comprising at least a paper machine and a multi-nip calender. The method comprises following steps: removing water from a formed paper web by pressing, drying the pressed paper web by at least one dryer, calendering the dried web by the multi-nip calender, measuring a cross-machine moisture profile or a variable relative thereto, and altering the moisture of the web so that the moisture profile of the web in the cross-direction is even when the web enters the first nip of the calender.

Description

background the invention

The The invention relates to the manufacture of high gloss, high quality magazine paper grades using online calenders. When online calendering is the calender arranged directly after a paper machine or a coater, and the web is also fed directly to the calender. These Kind of smoothed Papers were previously made by offline calenders and usually two or three calenders were used to work on one Handle production line produced paper, the paper rolled before calendering. The speed of older supercalender has limited their use as an online calendar. However, it has the Today's development of modern supercalenders and new multi-slit calendars allows the operating speed of these calenders to the level of Production speed of paper machines and coaters to increase, what made it possible to use these calenders also in online arrangements. All multi-slit calenders include several press nips made of soft and hard rolls are formed. The outer surface of the soft rolls is made of paper or other solid pulp or a suitable polymeric material. The hard rollers are made of steel, and most of the hard rollers can handle oil, water vapor or by other means, such as by electrical induction be heated.

Of the The purpose of calendering is to provide smoothness, shine and other properties the printing surface of the paper. To improve these improved properties of the printing surface the final quality of the printed sheet. The printability of paper and the quality of the printed surface are main quality factors, which is appreciated by the paper user become.

Reached will be smoothing the paper surface, by the fiber structure at the same time a high pressure and a Heat is exposed, resulting from heating up the hard rollers and Compressing the rolls is achieved so that a large liner splitting force on the Press nips between the rollers is generated. Under the influence of these forces the fibers forming the paper reach their glass transition temperature, wherein the deformation caused by the press nip load is stable. The gliding of the paper surface on the roll surface may also cause the fibers to deform and the smoothing effect strengthen.

If Multi-nip calendering was applied, the paper was on conventional Made in a paper machine and, if desired, then coated. In both cases the coated or uncoated paper was stored on storage rolls wrapped and smoothed in separate calenders. The paper was on dried a very low humidity, typically calculated at 1-3% from the total weight of the paper. Before the calendar becomes the paper rewetted to a higher one Moisture content for Good calendar results are required, typically up 6-10% calculated from the total weight of the paper. The reason for drying At a very low moisture content is the moisture profile over the Machine cross section (CD) to compensate. The short storage on Storage wrapping before calendering equalizes the moisture of the paper on the roller as well as the rewetting before calendering. In current online calendering concepts the paper is given a very low moisture content before calendering dried and moistened immediately before calendering. The process is therefore almost the same as offline calenders, but without moisture compensation memory.

The rewetting can e.g. with water spray devices described in U.S. Patent 5,286,348 in which a rewet device to get a good moisture profile in the cross-machine direction to obtain.

The with drying and subsequent rewetting The problem associated with the paper is the time the paper needs To absorb water and moisture for balancing, in particular in the direction of paper thickness and about the surface area the train. When the rewet Just before calendering, the uneven moisture profile will be the ultimate surface properties of the paper produced and the quality rating of the paper is diminished. As previously stated, the paper wraps after rewetting wound up and transferred to the moisture balance to the waiting station, after which the rolls were taken to offline calenders for the last calendering, to produce a high gloss and to densify the surface of the paper. In these offline systems, there was no need to improve the Moisture control because traditionally supercalendered Paper types like SCA and LWC in offline calenders at lower Speeds were smoothed as the speed of the paper machine and enough There was a time to equalize the moisture on the storage wraps.

The drying and rewetting process increases the energy consumption and space required for papermaking compared to a process without rewetting and over-drying before calendering. A non-uniform moisture profile results in uneven gloss and uneven strength profiles due to the influence of moisture on fiber formability. If the thickness profile is uneven, this causes difficulties in winding and may even cause transverse unevenness in the customer roll. The CD unevenness reduces the running properties of the paper in the printing presses and processing machines and in this way reduces the quality of the material from the customer's point of view.

The Moisture profile affects many factors of the papermaking process and the properties of the paper. A very remarkable feature is that if moisture profile differences in the paper are present, The drier parts of the paper are more likely to start entering and they go in more than the damp parts, causing the wet to stretch Parts leads. The uneven stretching leads to Entering the dry parts and stretching the wet parts, what further to strength fluctuations, Dehnschwankungen and variations in paper properties leads. A more detailed description of the influence of moisture and humidity fluctuations is given with the detailed description of the invention.

The Moisture profile of the paper being manufactured becomes currently controlled in various ways, especially at the beginning of the formation of the web. The purpose of controlling the moisture profile in current technologies is a good runnability to secure the machine and the product being manufactured. That is understandable, as a strong link exists between the moisture profile and the tension profile. In offline calendering, the moisture profile is preferred in those parts of the manufacturing process as even as possible, where the influence of the tension profile on the ability to run is the biggest. The ones caused by moisture variations and the tension profile Tension in the web does not affect the properties of the web As such, because the voltages during the waiting or storage time have time to relax before calendering. The normal waiting time in paper mills for off-line calendered Paper producing amounts approximately 1-5 hours. current Take into account moisture control procedures not the requirements of multi-slit online calendering and therefore can the quality calendered paper is detrimental to current moisture can be influenced, and therefore the quality of calendered paper can even by current ones Humidity control procedures be adversely affected.

The US-A-4,378,639 discloses a method of making smoothed paper by an online manufacturing system comprising at least one paper machine and a multi-nip calender, which method comprises the steps of Dehydration from a formed paper web by squeezing, drying the expressed Paper web with at least one dryer and calendering of the dried web comprising the multi-nip calender. According to US-A-4,378,639 the machine cross section moisture profile of the web at the dry end the drying section of the paper machine measured and the moisture profile the web will be at the wet end of the paper machine in one area varies where the moisture content of the web is at least 25% to ensure that the moisture profile of the web is even when the web in the Calender enters.

Summary the invention

Corresponding of the present invention is the cross-sectional moisture profile the produced paper web at at least one point in the production machine measured and the moisture of the web is in a drying phase varies in which the solids content of the web is at least 85% by Water is applied to the web as mist or spray, so that the moisture profile of the web is compensated before calendering and a best possible Calender result is achieved in an online Mehrspaltkalander.

The Moisture profile measurement can be done directly or by measuring a value that indirectly indicates the value of moisture. One such indicator is for example a web tension corresponding to The railway moisture varies because the strength of the railway is in line with its Moisture content varies. The web moisture measurement can Any position of the production line, but to a uniform cross-sectional moisture distribution to reach the calender must have at least one moisture measurement point be positioned at the end of the machine in an area in front of the machine last device that affects the moisture profile, and in front of the winding machine.

The Invention offers, among other things, the following advantages. It exists no need to dry and then rewet the paper, which is why the energy consumption is smaller and the machine is built shorter can be. The strength profile and the gloss of the paper is improved. The runnability of the Paper in the printing press is better and overall customer quality can be increased become.

Other objects and features of the invention will become apparent from the following detailed description in conjunction with the accompanying drawings. It should be understood, however, that the drawings are intended for purposes of illustration only and are not intended to serve as a definition of the limits of the invention, which are to be accorded the appended claims.

Short description of Drawings:

1 Figure 3 is an illustration of the influence of machine cross-section moisture variation on a web to be made.

2 is a schematic view of the embodiment of the invention.

3 shows a schematic side view of an apparatus which can be used to practice the invention.

4 shows a schematic plan view of an apparatus that can be used to practice the invention.

5 schematically shows a detail of in 3 and 4 shown device.

6 is a table showing typical types of paper that can be made according to the invention.

Detailed description the present preferred embodiments

Current moisture profiling strategies consider not the influence of the profiling on the structure of the final product and the further process potential. The importance of remaining in the paper Tensions and its possible Structural defects is reinforced in an online calendering process, in which the stresses before the Do not have time to relax, since calendering is few Milliseconds are done after the web is the last drying device leaves. Given the morphology of the fibers, the behavior of the fiber web can be when drying according to the solids content of the web divided into stages become. When the solids content is 50-55%, the solids content increases without changes Fiber morphology. If the solids content is 50-55% up 60-65% increases, the fibers begin at the fiber crossing points (connection points) to flatten, whereas on the surface of the web no changes result. When the solids content is 60-65% to 70-75%, wrinkles begin in parallel to the longitudinal axis of the fibers are aligned to emerge and the flattening of the fibers continues. At solids contents from 70-75% up to 80-85% the fibers start moving transversely to their unconnected Parting, the flattening of the fibers continues and the longitudinal wrinkles increase. When the solids content on 80-85% up to 90%, the fibers also start in the transverse direction to enter connected places, which sets transversal away and the wrinkles can be clearly seen. The morphology of the railway reaches its final Form at solids contents of about 90%. The taking of individual Fibers are the most significant at solids contents of 60-85%.

at Twin-wire machines start entering earlier than single-wire machines. For twin-wire machines, the starting point is around 55% solids and in single-screen machines at about 65%. For both machine types the stepping in the cross-sectional direction is from the beginning of the action continued until the end of drying. The growth of the action is approximate a linear function of the solids content. The values shown are averages and the wood / fiber material, the manufacturing process and the solids mass and their handling influence the solids content values, where the changes the morphology take place.

The Theory behind the morphology of the fibers gives the following possibilities to control the humidity profile.

method A

A leveling of the moisture profile before the strong penetration of the paper means means. that the measurement and adjustment of the moisture profile must be made in the moisture press zone of the paper machine and the solids content is at most about 60%, depending on the variety being produced. This method is preferable for several reasons. If there are significant changes in the moisture of the paper as it begins to enter, the drier parts begin to enter sooner than the moister parts (see 1 ). The moist parts expand in the cross-sectional direction and the drier parts enter and become denser. This can lead to fluctuations in intensity, fluctuations, drying and fluctuations in the properties of the paper produced. The entering of the paper is in the same physical phase as the so-called phase of decreasing evaporation rate. Typical of this phase is that the surfaces of the web are nearly dry and the middle part is much wetter. In this phase, the surface carries most of the forces imposed on the web in the direction of the machine. If water is added to the web at this stage, the water will break bonds between the fibers, this part of the web will weaken considerably in proportion to its environment. That's why one will large insertion and expansion surface induced in the vicinity of this area.

The uniformity the properties in the cross-cutting direction of the paper, which in the Drying stage of the paper are an essential Requirement for the paper to be in the calendering stage at the Production of e.g. onlinegeglättetem SC paper enough can be pressed. If that can not be achieved and significant Variations in the strength, the Modulus of elasticity, the drying input or the density before calendering, that will make it difficult to make large machine wraps. More importantly, in the worst case, the quality of the Customer's supplied paper.

In a solids content range from moisture squeezing to about 60% can be based on adjusting the moisture profile the following mechanism: by moistening with water or steam, by treating the web with hot or cold air Infrared dryers or by microwaves or differentially heatable or coolable Cylinder. The water and steam treatment processes may be called humidification processes and the other methods are based on either increasing the evaporation rate of water from the web or reduction the same by cooling the train. Examples of suitable devices will be shown later.

method B

The Moisture profile control should be in the range of 60-85% solids with methods based on temperature control as by treatment the web with hotter or cold air, by infrared dryers or by microwaves or by heatable or coolable Cylinder performed become. Humidification procedures should be considered due to correlations with Strong involvement in this area is not used in this area become.

method C

If the solids content over 85% is, can all methods used for use in method A are suitable because there is no significant engagement. This Solids content range represented also the solids content of a web which is coated, which is why for coating machines same profiling method can be used. If coated paper is made, it is important that the Adjustment of the moisture profile at the latest after the last coating station carried out because the wet coating mixture can change the moisture profile, e.g. due to fluctuating absorption characteristics of the base paper.

Whole moisture profile control concept for a paper machine

An embodiment of the invention is shown schematically in FIG 2 shown. 2 describes a squeezing section of a paper machine and subsequent dryer groups. The dryer groups may consist of drying cylinders, infrared dryers, air dryers, other dryers, or they may be a combination of commonly used types of dryers. Drying levels (DMC, solids content) at different stages of web formation are shown at the bottom of the figure. How out 2 As can be seen, the solids content of a web leaving the press section of a papermaking machine is 40-55%, and after the first dryer group the solids content increases to about 60% and increases gradually as the drying process progresses. At locations D and / or E, the web can be dried to a solids content below the moisture at which the paper is actually used.

The moistness pressing after formation of the paper can be carried out with conventional presses or preferably with a modern shoe press, since the shoe press effectively balances the small moisture fluctuations. Moisture profiling can be done on the squeeze section by profiling rollers or by steam. In this case, the profiling means are controlled by measuring instruments located at position A. The measuring method may be a humidity measurement, temperature measurement, voltage measurement or another method that displays the moisture profile of the web in the machine cross-section. A very suitable method for measuring and controlling different parameters in the papermaking process is in the US 5,649,448 shown. At points A and / or B there may be a humidity adjuster as used in Method A. The adjustment device is controlled by a forward or a feedback control method, or both, depending on whether the measurement of the moisture profile is made before or after the adjustment device. At locations C and / or D, a moisture adjustment device used in method B can be used. The adjusting device is controlled as described above by means of the measurement results.

At locations D and / or E, an adjustment device may be arranged according to method A. The device may be a moistening device, such as a water or vapor deposition device, only if the structure of the paper survives treatment by the device and the desiccant content is at least about 85%. It is considered that the structure of the paper survives the application of wetting if the amount of water used and the solids content allow the use of the device without the effects described in the description of method A.

To Position E can be the train dependent from the type of paper to be produced to an online multiple-calendar or transferred to an on-line coating machine. The moisture profile must be controlled, even during the Coating and all adjustment devices can be used as the Solids content of the web during coating normally greater than 85% is because the web is already at a lower moisture content while the formation and drying phases was dried. The following will be various methods described for moisture profiling are suitable. These methods and devices are suitable for Moisture adjustment in both paper machines and coaters, if the limitations described above are taken into account. The following described methods and apparatus may alternatively or simultaneously to be used.

One Profiling steam box controlled by transverse profile measurements, which are arranged after the Profilierungsdampfbehälter can be used in the ejection section of a paper machine. The steam tank is advantageously below the first drying cylinder group and the measurements are advantageously moisture profile, Tension profile or temperature profile measurements or a combination of these measurements. As in paper machines quality control and control systems already represent several measuring instruments, are all these measuring methods easily adaptable to new regulations. The CD temperature (cross direction temperature) can either by cooling controlled by the railway or by their heating. The temperature adjustment can at least one, preferably the last of the drying cylinder groups take place to a uniform To achieve temperature profile in the cross section of the web. The temperature measuring unit can after the CD temperature adjustment unit in or between the drying cylinder groups or arranged after the last drying cylinder group.

Moisture profile adjustments before the last drying cylinder group are also applicable by Profiling the surface temperatures the drying cylinder and / or by using profiling infrared drying units to adjust the moisture of the web and / or by using Rückbefeuchtungsausrüstungen for profile corrections. The temperature and / or moisture profile measurement can be done with instruments carried out are arranged in or after the last drying cylinder group are. Since the humidification and heating methods the dimensional stability and water absorption properties can affect the railway, offers the cooling the railways advantages over such procedures as the influences of cooling on the mentioned Properties of the web are smaller than those of moistening or heating process. If for profiling cooling is used, the temperature of the drying sections of the web is lowered, why the evaporation decreases. This procedure affects the Properties of the fibers minimal. The temperature adjustment can take place in different ways, e.g. by partially cooling one Drying cylinder with air or very fine water vapor from evaporates without significantly moistening the web. The influence of water cooling based on the for needed the evaporation of the water Energy. The profiling by means of cooling can also be done by cold Air is blown from a permeate discharge air dryer. If the profiling takes place successively in several places, can the moisture profile can be controlled with little change without damaging other important properties of the railway. The Orbit may also be due to the machine temperature or the temperature of the machine housing cooled down the calender unit be to the progress of the drying of the paper between calender and last drying plant to prevent. This prevents uneven moisture evaporation from the railway before calendering. When the web enters the calender, is the preferred moisture content 7-20% calculated from the total weight the train.

A Last moisture profile adjustment can also be done by applying be carried out by water in the form of steam, spray or a thin film, that on the paper in a calendering column or through a surface calibration unit within a drying cylinder group or between the last Drying cylinder and the calender is applied. In this Case may be the CD moisture profile measurement immediately before the calendar or after the calendar in front of the winding unit be arranged. A film transfer unit or a surface calibration unit can be used for moisture profiling by control the strength of the water film, the film size applied to the film transfer roller.

3 - 5 show schematically a Profilierungsgebläsebehälter that can be used either for cooling or for heating a web. The container comprises a housing 1 that has a nozzle surface 2 forms, which is formed, a roller to reproduce over which a train is running. Air or steam can enter the case 1 through the coupling 3 blown and selbiger) is from the housing 1 through the nebulizer nozzle surface against the web. The nozzle area 2 comprises an arrangement of movable bands 5 which are arranged to move between guides or rails. One end of the bands is about a drive shaft 7 wound, which is divided into sections, so that each band has its own drive section. By rotating the drive section, it is possible to move the belts between the rails so that they cover different lengths of the surface of the approach surface. If the bands are narrow, eg 10-100 mm wide, the device can be used to compensate for small fluctuations in the moisture profile. With other devices, it may be difficult to obtain such finely graded profile control as with this device.

The Moisture profile control and adjustment is preferably performed performed more than one of the previously described ways. If Various correction steps are used, the need for larger adjustments avoided in one step and the influences on the procedure and the Paper is smaller. Likewise, the control of the device becomes easier.

The invention can be used for several types of multi-nip calenders characterized by multiple calender nips and relatively high nip loads. Examples of these types of calenders are supercalenders, Janus concept calenders (see Paper Asia, Oct. 1997, Examination Cards No .: 10/007), a calendar shown in U.S. Patent No. 5,438,920, or other types of multi-nip calenders used to make Glossy paper types are used. Examples of paper grades suitable for the preparation according to the invention and their properties are in 6 shown, which is self-explanatory.

Claims (17)

Method of making smoothed paper with the help of an online manufacturing system comprising at least one paper machine and a multi-nip calender with press nips formed from soft and hard rolls, wherein the method comprises: - Remove of water from the formed paper web by means of pressurization, - Dry the pressed paper web with at least one drying device, - smoothing the dried web with the multi-slit calender, - Measure up a moisture profile in cross-section or related thereto Variables, and - To adjust the moisture of the web in a drying phase, the solids content the train is at least 85%, in which water is applied to the web as a mist or spray, such that the moisture profile of the web is uniform in cross-section, when the web enters the first nip of the multi-nip calender. The method of claim 1, comprising: - additional Adjusting the moisture profile by at least one damper, the is arranged in the pressing section of the paper machine, and - Measure up the moisture profile in cross section or a related Variables at a downstream Place of the profiling damper and preferably after at least one drying device, the follows the pressing section. The method of claim 1, comprising the adaptation the temperature of the web to control the rate of evaporation of the water from the web, further controlling the moisture profile of the web becomes. The method of claim 3, wherein the temperature is Cool the web at least about a cross-sectional width of the web is adjusted. The method of claim 3, wherein the temperature is Heat the train over at least one cross-sectional width of the web is adjusted. The method of claim 3, comprising measuring the Temperature profile of the web in cross section, behind the temperature changing Device either immediately after this device, between the drying devices or subsequently the last drying device in front of the calender. The method of claim 6, comprising measuring the moisture profile of the web over the cross section of the web both immediately following the temperature changing Device, between the drying devices or below the last drying device before the calender. The method of claim 1, wherein the moisture the railway also over the cross section of the web is changed before the drying phase, wherein the solids content of the web is at least 85%, by means of at least one device from a group consisting of: a Drying cylinder, an infrared dryer, a moistening device, a damper, a penetrating air blower, one profiling fan box or a water applicator. The method of claim 8, wherein the moisture profile or a related variable within a last group of drying devices or following the cylinder group measured in front of the calender. The method of claim 1, comprising cooling the Trajectory after the last drying device to the ambient temperature, for an uneven evaporation to prevent the water from the web. The method of claim 1, wherein the moisture profile is above the Cross section immediately before the calender or following the calender before a winding device is measured. The method of claim 1, wherein the moisture profile the web moreover is adjusted in a drying phase, wherein the solids content the train is 60% or less. The method of claim 12, wherein the moisture profile is adjusted in the drying phase, the solids content the web is 60% or less, through at least one device the group of: a water application device, a vapor deposition device, a hot air box, a cold air box, an infrared or microwave drying device. The method of claim 1, wherein the moisture profile the web is further adjusted in a drying phase, wherein the solids content of the web 60-85% is. The method of claim 14, wherein the moisture profile is adjusted in the drying phase, the solids content the railway 60-80% is, by at least one device from the group of: a Heißluftbox, a cold air box, an infrared or microwave drying device. The method of claim 1, wherein the web has at least a coating layer in an on-line coating machine coated in front of a calender. The method of claim 2, wherein the method comprises: - changing the Temperature of the web to the evaporation rate of water from the To control the railway - Measure up the temperature profile of the web in cross section after the temperature changing Device either immediately after this device, between the drying devices or subsequently the last drying device in front of the calender.